1. Field of the Invention
The subject invention relates to an actuator for turbomachinery and an application thereof. More particularly, the invention relates to an actuator for turbomachinery that includes an improved piston ring configuration for sealing between the actuator's piston and cylinder, and an improved method for actuating adjustable seals in turbomachinery.
2. Description of Background
Fluidic actuators within turbomachinery are typically exposed to a harsh environment of very high temperatures and pressures and employ high actuation pressures of up to 3,000 pounds per square inch to move components such as packing rings and adjustable seals.
One factor that limits the amount of force an actuator can apply is the effectiveness of the sealing of the actuator. The more effective the sealing, the lower the leakage of actuation fluid, and the higher the possible actuation force. As sealing becomes less effective, lower actuation forces are possible with each actuator, thus a greater quantity of actuators must be utilized to move a desired component. If more effective sealing is achieved, it is possible to increase the amount of force applied by each actuator and therefore the number of actuators required to move a desired component may be reduced.
A bellows actuator is one type of actuator that is used in turbomachinery applications. A bellows actuator includes a cylinder with a piston disposed therein and a bellows connecting the piston to the cylinder, providing sealing between the cylinder and the piston, and thus creating a high pressure region and a low pressure region. With the bellows in place, there is effectively zero leakage between the high pressure region and the low pressure region. However, the bellows are susceptible to failure by conditions such as overpressurization of the actuator, reverse pressurization across the actuator, side loads, moisture in the actuation air, debris in the operating environment, and other conditions, that limit the life of the bellows and consequently the effective life of the actuator. Failure of the bellows may lead to a reduction in the maximum actuation force that the actuator can reliably apply, or an entirely nonfunctional actuator.
An alternative to the bellows actuator is the piston ring sealed actuator. Like the bellows actuator, the piston ring sealed actuator includes a cylinder with a piston disposed therein. In this case, however, the sealing is provided by one or more piston rings inserted into a piston ring groove or grooves in the piston, or alternatively inserted into a groove or grooves in the cylinder. While a piston ring seal is less susceptible to failure than a bellows seal, at the high pressures and temperatures present in the turbomachinery environment, a typical actuator with a piston ring seal is susceptible to leakage between the piston ring and the cylinder wall, and between the piston ring and the piston ring groove. Because of this leakage, the actuation force of an actuator with a typical piston ring seal arrangement is also limited, and more actuators than desired are needed to move components within the turbomachinery. Furthermore, more actuation fluid is needed to provide the desired actuation.
As indicated above, it is advantageous to have actuators with a long useful life that exhibit nearly zero leakage in the high pressure, high temperature environment inside of turbomachinery. With longer life and more effective sealing, higher actuation forces can be applied to the actuator, thus reducing the number of actuators required to move a desired component. Low leakage actuators also require less actuation fluid, which makes the overall actuation system design simpler. What is needed is an actuator seal configuration with long life and exhibiting nearly zero leakage from the high pressure side of the actuator to the low pressure side of the actuator.